Safety studies on fuel element behaviour in a pressurized water reactor core using computer programs

The computer codes SPAGAF, DRUCK, and AFBETA were written for evaluating the thermal and mechanical behaviour of fuel elements and the fission product distribution within the core of pressurized water reactors during normal operation and accidents. Based on a cylindrical fuel rod, the SPAGAF code calculates the interactions between mechanical changes of fuel and cladding and the temperature profile. As compared with experimental data the results of test calculations show that the deviations obtained from SPAGAF are in a range acceptable in safety studies. The DRUCK code gives information about failure probability of fuel cans during a loss-of-coolant accident. The changes in fuel element internal pressure obtained by means of DRUCK for the blowdown phase of a LOCA suggest a burst rate of less than or equal to 1%. Consequently, no significant damage to the core is to be expected during the blowdown phase. Following these calculations, the AFBETA computer code simulates the local and time-dependent in-core distribution of fission nuclides, especially the nuclide transport from the fuel void volumes of the fuel element and, in the case of failed fuel cans, through the leak into the coolant. (author)